This invention relates generally to underground pipelines, and more specifically to maintenance and testing of underground pipelines.
Pipelines and other metallic structures are inherently inclined to corrode. The corrosion process involves the removal of electrons or oxidation of the metal, and consumption of those electrons by some other reduction reaction, such as oxygen or water reduction. Corrosion is encouraged by the presence of moist soil in contact with a metal pipeline.
The electrochemical nature of the corrosion process provides opportunities to detect and mitigate corrosion of underground structures. Typical mitigation methods include applications of coatings to the structures and neutralizing the voltages and currents associated with the corrosion process through application of external voltages and currents.
Corrosion mitigation processes can be monitored to determine the extent of corrosion activity and to verify the effectiveness of electrical corrosion prevention systems. One known electrical corrosion prevention system for application of external voltages and currents to an underground structure, such as a pipeline, is referred to as a cathodic protection system. As part of the maintenance process, corrosion mitigation processes are monitored to determine the extent of corrosion activity. As a result, effectiveness of the cathodic protection system is also monitored.
The U.S. pipeline industry has standardized methods for assessing the performance of a cathodic protection rectifier system. One method used to detect corrosion activity and to assure the proper performance of the cathodic protection systems includes reading and verifying the output voltage of cathodic protection rectifiers, and reading and verifying the impressed current on the pipeline by measuring the voltage drop across a shunt resistor connected in series with the output of a cathodic protection rectifier. U.S. governmental regulations currently in place require measurement of rectifier voltage outputs at least once every two months.
Another conventional pipeline test, sometimes called an xe2x80x9conxe2x80x9d potential measurement, includes reading the pipe-to-soil voltage at test points along the pipeline with cathodic protection rectifiers turned on, and verifying a potential between the structure and a reference electrode in the ground adjacent to the test point. One known U.S. testing standard requires verification of at least 850 mV between the structure and the reference electrode.
One proposed testing methodology includes reading a polarized voltage of the pipeline by reading the pipe-to-soil voltage at test points along the pipeline (typically located 100 yards to 1 mile apart) 100 msec to 1000 msec after all cathodic protection rectifiers affecting the test point have been simultaneously turned off. Such a test is sometimes referred to herein as an xe2x80x9cinstant offxe2x80x9d potential measurement. The polarized voltage is a measurable potential between the structure and a reference electrode in the ground adjacent to the test point. Such a test would attempt to verify at least 100mV between the pipeline structure and a reference point.
Another test, sometimes referred to as a close interval survey, involves measuring potential differences at very close intervals (around 3 feet) between the pipeline structure and adjacent soil both with cathodic protection rectifiers turned on as well as an instant after the rectifiers have been simultaneously turned off. Current close interval survey testing seeks to verify at least 100 mVolts of potential between the soil and the pipeline structure. However, conducting close interval surveys is a highly manual process, with a potential for errors, as described below. Therefore it is typical to only accomplish a close interval survey of about 20% of a pipeline in any given year.
When conducting close interval surveys, the current applied by all rectifiers affecting a particular segment of pipe are synchronously turned off and on (cycled) so that an applied voltage and a polarized voltage are recorded. Usually, survey crews are used to set up synchronized interruption equipment at each rectifier. The equipment initiates synchronized cycling and then the pipe to soil potentials are measured. Following the survey, the team returns to each rectifier location where synchronizing equipment has been temporarily installed to verify that the cycling activity occurred as expected and to remove the equipment for installation at a different pipeline segment. If the team cannot verify that the cycling activity was properly conducted at each rectifier location, the resulting collected data is rendered questionable and the survey may have to be repeated.
Underground pipelines may be adjacent to or near other structures which have ground contact and are therefore subject to corrosion. Cathodic protection systems sometimes are provided fir such structures. The structure, as well as its protection system, may interfere electrically with the cathodic protection systems for the pipeline. The interference is typically manifested as undesired currents flowing between the pipeline and the structure. To control such currents, a shunt resistance may be placed between the structure and the pipeline. Such an installation is sometimes referred to as a critical bond. Testing of critical bonds is performed to ensure that the corrosion mitigation processes in place continue to be effective, and simply to verify that the current path between the structure and the pipeline has not been opened.
There is an increasing interest in checking the polarized voltage (or instant off potential) at pipe-to-soil test points as well as the constant potential at these sites. The polarized voltage tests supply pertinent pipeline corrosion data. Further, close interval surveys are becoming more common. However, the above described testing, as currently performed, is largely manual, and difficult to synchronize, utilizing known testing equipment.
In one aspect, a method for testing a cathodic protection system is provided. The system includes a cathodic protection rectifier configured to apply a voltage between a pipeline and a reference point. The method comprises measuring a magnitude of an output voltage of the cathodic protection rectifier and transmitting the measured output voltage magnitude to a site remote from the rectifier using a cellular control channel. The transmitted measurements are received at the remote site and using the transmitted measurements, it is determined whether the cathodic protection system is operational.
In another aspect, a cathodic protection rectifier system for an underground pipeline is provided. The pipeline is configured with a plurality of testing points. Each test point is an access point for making measurements and is electrically coupled to the pipeline. The system comprises at least one cathodic rectifier coupled to a power source and configured to apply a voltage across the pipeline and a ground reference point in the soil. A cathodic system monitor is coupled to the rectifier and configured to act as a switch between the rectifier and the pipeline. The cathodic system monitor is further configured to receive primary power from the power source, and to measure voltages applied to the pipeline. The cathodic system monitor also communicates the voltage measurements as pipeline test data. The system also includes a computer system configured to receive the pipeline test data from the cathodic system monitor.
In another aspect, a method for testing effectiveness of galvanic corrosion mitigation equipment along a length of an underground pipeline is provided. The equipment includes at least one cathodic protection rectifier (CPR) electrically coupled across the pipeline and a reference point through a switching device. The CPR is configured to apply a voltage to the pipeline. A plurality of test points are electrically coupled to the pipeline and dispersed at intervals along the pipeline, providing an access point for measurements. Near each test point is an reference point, which provides an electrical reference for the test point. The switching device is controlled by a cathodic system monitor which also includes a cellular modem and is configured to communicate with an external system. The method comprises applying the CPR voltages to the pipeline, measuring an output voltage of each CPR, measuring a voltage present at each test point, the voltage being measured by a test point monitor located at each test point, each test point monitor including a cellular modem and configured to transmit the voltage reading to an external system, transmitting the voltage measurements to the external system and analyzing the voltage measurements utilizing the external system.
In still another aspect, a cathodic protection system is provided. The system comprises a plurality of cathodic protection rectifiers, a plurality of switching devices, a plurality of GPS interrupters, a plurality of cathodic system monitors, and a plurality of test point monitors. The plurality of cathodic protection rectifiers are spaced at intervals along a pipeline. Each of the switching devices is configured to electrically connect one of the rectifiers to the pipeline. Each GPS interrupter is configured to control operation of at least one of the switching devices. Each of the cathodic system monitors is configured to measure an output of one of the cathodic protection rectifiers, control operation of one of the GPS interrupters, and communicate with an external system utilizing a cellular control channel. The test point monitors are spaced at intervals between the cathodic protection rectifiers, and are electrically connected across the pipeline using test points. A reference point in the ground provides a return path for electrical measurements at the test points. The test point monitors are configured to communicate with the external system utilizing a cellular control channel.
In yet another aspect, a method for performing a cathodic protection system test utilizing a plurality of test points electrically connected to a pipeline is provided. The cathodic protection system includes a plurality of test point monitors electrically coupled to various test points along the pipeline, the test points being electrically connected to the pipeline. The test point monitors are configured to communicate with an external system utilizing cellular control channel communications. A plurality of cathodic protection rectifiers are electrically coupled to the pipeline through switches, the switches being controlled by a GPS interrupter. The method comprises configuring the test point monitors to measure a voltage at the test points, concurrently opening all switches which cause a voltage from cathodic protection rectifiers to be present at a test point, measuring the test point voltages with the test point monitors, concurrently closing all switches which cause a voltage from the cathodic protection rectifier to be present at a test point, measuring the test point voltages with the test point monitors, and transmitting the measured voltages to an external system over the cellular control channel.